Known Methods in Use Today
Today anodes (electrodes) are produced by the use of electrolytic coating a substrate with thin layers of precious (noble) metals. However these electrodes have a particularly short lifetime and they do not tolerate being exposed to high voltages over time. If they are exposed to high voltages they will burn. During the process a dissolving/-precipitation occurs from the anode so that it is corroded.
There is also a production of anodes of pure metals or alloys of such metals, and which do not belong to the precious metal group, but these are quickly corroded in use, they do not produce the desired oxidant, nor can they be exposed to the desired voltage.
Another lesser-known method in use today involves that tantalum, iridium, or a mixture of these are rolled down to between 0.015 and 0.035 mm and is welded to a core for an anode which is made of titanium, aluminum or copper. By this method a frictional welding is used. The lifetime for these electrodes is longer than of the electrodes that are made by use of electrolysis. They tolerate substantially higher voltage and current. With these advantages in variables for electrolyses process, i.e., voltages from 0-380V and currents from 0-1000 Amperes, a mixture of oxidants is produced including a very high reactivity, power and possibility for functional balancing of the single oxidants (Cl2, ClO3−, O3, O2, H2O2, OH, ClOH, O), exceeding the effect of, and reduces the undesirable effect of oxidants from anodes produced by other methods.
The limitations for the preparation by these methods are the variation span in the mixture of alloys. For example it is known that platinum/iridium-alloys (Pt/Ir) including more than 20% iridium is difficult to roll down to the desired thickness. Today it is known that the alloy can be rolled down to 33 micron (0.033 mm). Higher concentrations of Ir leads to even greater problems, and the prepared foil often becomes brittle. It is also desirable that the foil have a high degree of hardness in order to increase the mechanical resistance to wear and tear. Further the thickness of the foil is decisive in determining how much of certain oxidants is produced in a certain liquid with a given voltage and current. It is further known that for example pure platinum technically may only be rolled down to 15 micron (0.015 mm). Below this thickness it is not possible to obtain a dense foil (without pores).
Recently methods for vacuum/plasma spraying of tantalum and precious metals according to the abovementioned method have extended the potential of use in that methods for spraying of thinner layers have been developed, and at the same time increased the variation span of the mixture of an alloy with 100% pore density, and thus the specific area of use has been extended.
The known electrolytic processes in its simplest form provide Cl2 as an oxidation agent. Further oxidants (ClO3−, O3, O2, H2O2, OH, ClOH, O) are however far more chemically reactive, and are provided by coating a substrate with precious metals where a voltage is exposed in a range where the law of Farraday is exceeded.
Of these components the radicals are in particular the most powerful oxidation agents, both with regard to power and non-desirable side-effects (halogenated compounds of organic material). The problem of the known electrolytic processes is that the radicals cannot be utilised since they have a lifetime of a thousandth of a second and are therefore only present very close to the surface of the anode. As only a very small part of the liquid amount that is conducted through an electrolytic cell makes contact with this anodic surface, large amounts of liquids cannot effectively be exposed to radical exposure for reaction with organic compounds, bacteria, virus etc, which is desired to be eliminated from the liquid.
Known electrolytic processes form hydrogen at the cathode. Hydrogen lowers considerably the formation of oxidants by the anode since the hydrogen forms water when it comes in contact with the oxidant. This applies in particular to OH-radicals in contact with hydrogen. The hydrogen gas also reduces the conductivity of the liquid when it is present in the voltage field between the anode and cathode, and in contact with the anode.
It is known from U.S. Pat. No. 6,328,875 that electrolytic cell designs have been developed with anodes/cathodes made of conductive porous elements consisting of metal, including noble metals, or carbon from welded or woven wire cloth, expanded metal or carbon felt, carbon woven cloth or reticulated vitreous carbon and metallic foam. The structure includes an open solution where the effluent is passed in-between a spacer/anode and cathode to open area (open solution). The stack is clamped together and anode/cathode are separated, mono polar or bipolar, by spacer to prevent shortcut. The effluent is then passed in parallel with the anode/cathode/spacer in the process.
Furthermore it is known that U.S. Pat. No. 6,342,151 comprises anodes/cathodes made of permeable conductive material selected from the group consisting of perforated plates, screens, wool, felt and weave made of stainless steel, aluminum, copper, platinized titanium, mixed metal oxides, gold and gold plated steel. Also this electrode uses spacers to prevent short-circuits between anode and cathode when distance between said components is small.
It is well known that spacers increases current consumption in an electrolytic process and reduces flow capacity through the electrode.
It is also well known that fouling due to scaling caused by Mg and Ca content in the effluent treated is a substantial problem with respect to electrolysis. The scaling problem occurs when velocity of Mg and Ca contained effluent (such as sea water) is passed through an anode/cathode reaction. If the velocity of the effluent is too slow, a bridge of crystals will accelerating be built between anode and cathode causing fouling of the process. Increasing the velocity in such extent might prevent this in such extent that all Mg and Ca build up are transported away before it attaches to the cathode. Another way, provided that anode and cathode are of same or equal reactive material, is to alternate the polarity of the anode and the cathode regularly. Then scaling burst off the cathode as it is reverted to anode.